Method of preparing flotation concentrates



June 19, 1928. 1,673,891

H. J. STEHLI METHOD OF PREPARING FLO'IATION GONCENTRATES Filed July 50,1926 ATTORNEY Patented June 19, 1928 UNITED STATES HENRY J. STEHLI, OFCEDAR GROVE, NEW JERSEY.

METHOD OF FREPARING FLOTA'IION CONCENTBATES.

Application filed July 30, 1926. Serial No. 125,858.

By the modern methods of concentration of ores for the purposeofseparating values from the accompanying earthy material or gangue, theores are frequently ground to 1 almost flour fineness and the resultingconcentrates, after having as much water removed as possible b means offilters, are still wet and at best lilVe the consistency of soft putty.Ores of this character are usually sintered as a preliminary totreatment in smelting furnaces to remove sulphur if that is necessary,but chiefly to produce a coarse product favorable for subsequent blastfurnace smelting. Such ores may have to go through a considerable amountof handling before they are delivered to the sintering plant, and intheir wet, stick; condition are very difficult to put into an dischargeout of cars, draw out of hoppers or bins, or handle through chutes,elevators, conveyors, etc. The treatment which I describe below makessuch ores easy to handle, as they can be put in cars, bins, etc., or bedrawn out through chutes or conveyed in elevators or conveyors withoutsticking to the containers. As a requisite for successful sintering thematerial to be sintered should be fed onto the sinterin machine in aloose bed permeable to t e air currents. Such concen- 30 trates presenta diflicult problem, since in their wet plastic condition they do notoffer a mass sufliciently permeable to the air currents in the sinteringmachine, and if the concentrates are mixed up in some form of mixing ordisintegrating device the particles stick together again almostimmediately, giving an impervious bed, or at best, one that isirregularly permeable. The air currents, choosing the permeable spots,leave untouched the denser areas. This results in a very unsatisfactory,partially sintered product full of unsintered fines or of fines {ugh insulphur, which cause high dust osses.

,To avoid the foregoing objections the usual methodis to mix suchconcentrates with other materials. Such procedure is only partiallysatisfactory, as the resulting mixture contains a large proportion ofthe 5 lastic concentrates in relatively large l,; f;'.,'l umps, as fromthe size of an egg down to the size of a walnut, which have not becomebroken up and thoroughly mixed through the charge. Such lumps, becauseof their M impermeabilit'y to air, cause unsintered spots 01' islands inthe sinter bed, and, as a re sult, high sulphur content in the sintercakes and serious dust losses.

{is the tonnage of ores treated by the flotation process is dailygrowing greater, and the amount of other ores available to mix with themis daily growing smaller, the problem has reached an acute stage.

It is well known that a charge to successfully sinter must contain acertain amount of water, which may vary from 8% to 12%. It is, ofcourse, possible to subject the wet concentrates above mentioned whichcontam, as they come from the filters, 15% or moreof Water, to a processofdrying. In practice this is unsatisfactory not only on account of thecost but because such material cannot be readily dried to a uniformvmoisture content. It can be completely dried but the resulting driedmaterial consists of baked lumps which are hard to break up again, andwhen broken up they form fine dust. It is not feasible to stop thedrying at a point where the material will still contain from 8% to12%-moisture became this drying action is uneven. The partially driedmass would consist of some completely dried dusty material and aquantity of large lumps dry and baked hard on the outside and still verywet on the inside, making a material unsuitable for a sintering chargeand one which would be almost impossible to mix satisfactorily.

The object of the present improved method is to so treat and mix theconcentrates referred to that they will readily flow through bins,chutes, etc., and when fed on the bed of a sintering machine they willform a loose, open mass, readily permeable to the air currents, andwhich when sintered will give solid cakes thoroughly agglomerated andfree from dust.

In the preparing of concentrates I proceed as follows:

I divide the wet plastic ore concentrates or fines into relatively smalllumps, pellets, nodules or the'like of such a size, that they will givethe maximum of large air passages while at the same time be themselvesof a size such as to most efficiently undergo the desired reduction intreatment on the sintering machine, and I coat the lumps, etc., with asuitable dry powder-like or pulverulent material that 'will adhere tothe lumps and thereby keep them separated in the mass so that the lumpswill not stick to other and will thereby provide a permeab e mass inwhich spaces between the lumps will permit the assage of air. Thematerial for coating the umps or the like may comprise dry ore, fluedust, lime or any other suitable dry material, of which there is alwayssome to be found available among materials to be smeltered at anysmelter. Under some conditions it may be found desirable or economicalto dry a certain percentage of the concentrate to be sintered, say 10%,and use the same in powder form for the purpose of coating the lumps andthe like. The wet plastic concentrates may be divided into the smalllumps, pellets or the like by any suitable means. The wet plasticconcentrates may be forced through a machine on the order of theordinary meat grinder which will serve to divide or chop theconcentrates into small lumps or pieces, the size of which will begoverned by the character of the machine, or other well known machinesadapted for dividing masses into small pieces may be used for thepurpose. In order to economically and expeditiously coat the aforesaidlumps of wet concentrates the lumps, pellets or the like may bedelivered into a revolving drum containing the dry powderlike materialused for coating the lumps. and as the latter drop into the revolvingdrum they immediately begin to roll around in the powder and accumulatea coating of the dry powder-like material until the lumps are no longersticky on the exterior and will not pick up any more of the drymaterial. The drum may be provided with interior cups or shelves in thesame manner as in an ordinary concrete mixer, which mixer may be usedfor the purpose if desired. The cups or shelves, as the drum revolves,lift a certain amount of coated lumps, pellets or the like and also anamount of the dry material or ore up above the mass in the drum and pourthe. same out onto an inclined chute. The chute may have a perforatedbottom, such as one made of screen cloth, and maybe caused to shake insuch a manner that the dry material unattached to the coated lumps orthe like will fall back into the drum while the coated lumps will rollalong the screen-bottom chute and may be directed into the sinteringmachine hopper, or to any other desired place, whereby the coated lumpsare separated from the mass of dry coating material. The mesh of thescreen should be smaller than the coated lumps or pellets so that as thelatter run down over the screen and fall into the hopper of thesintering machine the excess of fine dry coating material will passthrough the screen and be returned to the mixing drum. If desired theaforesaid chute may have a solid bottom and the coated lumps and some ofthe dry coating material may be delivered from the chute' to an outsidescreen which will serve to separate the coated lumps from the remainingdry material, which lumps may pass to the hopper of the sinteringmachine in any desired way.

While some fine concentrates do not possess this sticky character-forinstance, the zinc flotation concentrates from the Joplin districttheynevertheless, because of the exceedingly small interstices between thevery minute particles, do not present good conditions for sintering.These passages between the particles are so small that the air currentscan be drawn through them (because of friction) only under anexcessively high suction. Such a high suction has a tendency to pull agood deal of the material from the bed at points where the coherence ofthe bed is the least, and the result is the production of flue dust andloss of values. Therefore, one of the main objects of my method is toincrease the size of the air openings through the one bed. The smallerthe nodules the smaller will be the size of the air passages, and thegreater the resistance to the suction. On theother hand, if the nodulesare made too large, or if the material is not nodulized at all, but fedon the bed in the shape of big plastic lumps, then while the individualair passages are large enough, they are not sufficiently disseminatedthrough the mass to produce even sintering and homogeneous sinter.

In the foregoing description it is to be assumed that the fines orconcentrates possess a suitable sticky or plastic character. whereby thematerial of the lumps will adhere together. Most flotation concentratescontain a certain amount of clayey matter or hinder which makes itpossible to produce the relatively small plastic lumps or nodules beforereferred to that can be rolled in the dry coating material. Some fineconcentrates do not possess such a sticky or plastic character, therebeing no such clayey binder present. For instance, in the zinc flotationconcentrates from the Joplin district, and because of the exceedinglysmall interstices between the very minute particles such ores do notusually present good conditions for sintering. The passages between thepar ticles are so small that the air currents can only be drawn throughthem under an exceedingly high suction which has a tendency to pull someof the material from the bed at points where the coherence of the bed isthe least, and the result has been the production of fine flue dust andloss of values To such a natural n0n-sticky or non-plastic concentratewater may be added to make momentary lumps but they will haveinsuificient coherence to hold their form during the rolling and coatingprocess I have described or during subsequent handling, so that whenthey break up they produce an exceedingly fine moist mass. In order toprepare such natural non-sticky or non-plastic fines or concentratesfor-the production of lumps to be coated with the dry powder 1 add tosuch concentrates a relatively small amount of plastic material, such asfire clay, whichneed not be more than 5%, (and frequently may be lessthan 5%), mix the mass, and add a suitable amount of water to themixture (if it. is not already present) to' impart to such naturalnon-sticky or non plastic flotation concentrates the desired plasticcondition which will make it possible to produce therefrom the lumps,nodules or the like previously referred'to of such a character that theywill retain their shape, and they may be treated in exactly the mannerpreviously described for coating the lumps with the powdered material.Such natural non-sticky or non-plastic concentrates are thereby producedin a. form in which sintcringmay take place much more rapidly than if nobinder is added because of free air passages between the lumps in thesinter bed,'whereas when such non-sticky fine concentrates are placeddirectly on a sinter bed they present exceedingly small intersticesbetween the very minute particles and do not present good conditions forsintering.

The lumps or pellets of concentrate coated with powdered material asdescribed will be wet. or damp on the interior, suitable for sintering.The dry coating will keep the lumps or pellets from sticking to ether orcoalescing into a solid impermeable mass.

Such coated lumps or pellets are fed into a sintering machine of anywell known make and will present a loose bed of substantially uniformpermeability with a multitude of air passages between the lumps orpellets which will be ignited, and said passages will facilitate thepassage of air currents through the sinter bed in the process ofsintering and thus promote uniform and rapid sintering of theconcentrates. For some cases it is desirable, while making a uniformlysintere'd product, to retain as much sulphur as possible in the sinteredproduct for subsequent reuses in a blast furnace. This is par-,ticularly the case with copper concentrates high in copper wheresulphur is required to make matte in the blast furnace. In other cases,such as, for instance, lead or zinc ores, it is desirable to eliminatethe sulphur as far as possible. These variations can be effected byregulating the size of the lumps or pellets according to my invention.The smaller the pellets are in size the greater will be the eliminationof sulphur in sintering, and the larger the size of the pellets thesmaller will be the elimination of sulphur in the sintering. It ismanifest, therefore, that in accordance with my method the metallurgisthas a means of regulating the sulphur content of his sinter within awide range, while at the same time always making a properly sintere'dproduct even when the material to be sintered consists of flotationconcentrates or similar materials comprising extremely tine orpulverulent particles and which are plastic when wet, because of theability to regulate the size of the coated over the present practice ofsintering ores of the character referred to herein. Furthermore, myimproved sinter cakes from such ores are more advantageous for use insmelters than the known sinter cakes because of the regularity of myproduct which will be more readily reduced with less ore losses, orirregular furnace operation, and at less costthan heretofore.

The accompanying drawing diagrammatically illustrates a machine in whichthe lumps, pellets, nodules or the like may be formed from theconcentrates and mixed with the powdered material for delivery to thehopper of a sintering machine. numeral 1 indicates a cylinder in which arotative screw or worm 2 is provide for forcing the material 3 to bedivided, such as lumps of concentrates and attendant fines, which aredelivered into the cylinder through the intake opening 4 and are forcedfrom the cylinder by the screw through any desired number of outletholes at-5. The delivery outlets 5 are shown located within a rotativedrum 6 into which the cylinder 1 extends through a. side opening 8. Thelumpslpellets or the like 3 drop from cylinder tlei'nto the drum, whichdrum is provided on its interior with any desired number of cups orshelves 7. At 8 is an inclined chute shown having a perforated portion 9within the. drum, the chute extending through the side opening 8 of thedrum, the outer portion 8 of the chute being shown imperforate so thatthe coated lumps or the like will slide along the chute for deposit asin a hopper 10 of a sintering machine, elevator, chute or bin. Thepowdered material for coating the lumps or the like is indi cated at 11within the drum, and when the drum rotates the lumps will be rolledaround with and within the powdered material for coating the lumps, andsuch material and the coated lumps will drop from the cups or shelvesupon the perforated portion of the screen, the material falling throughthe screen into the bottom of the-drum while the coated lumps or thelike slide down the screen to the hopper. Any suitable or well- Theknown means may be provided for shaking the screen. The screw 2 and thedrum 6 may be rotated in any well known or desired way.

Having now described my invention what I claim is:

1. The method of preparing plastic ore fines for sintering consisting individing a mass of wet fines into lumps and coatlng the lumps with apowdered material to prevent the lumps from adhering to one another andto provide air passages between the lumps in a mass.

2. The method of preparing plastic ore con'centrates for sinteringconsisting in dividing a mass of wet concentrates into small lumps andcoating the lumps with a dry powdered material to cause the lumps toremain separated in a mass with air passages between the lum s. r

3. The metho of preparing plastic wet material for sintering consistingin dividing a mass of plastic material into small lumps, dropping thelumps into dry coating material, moving the lumps and the said drymaterial about to cause a suflicient amount of the dry material toadhere to the surfaces of the lumps to prevent the lumps from stickingto one another, and then separating the coated lumps from the excess drymaterial.

4. The method of preparing plastic flotation concentrates for sinteringconsisting in dividing the plastic concentrates into small lumps,depositing the lumps in dry material adapted to adhere to the surfacesof the lumps, causing the mass of material and lumps to be rolledtogether until the lumps are coated with a sufficient amount of the drymaterial to prevent the lumps from sticking to one another, andseparating the coated lumps from the dry material.

HENRY J. STEHLI.

